<?php
/**
 * 判断一个坐标是否在一个由多个坐标围成的多边形内
 * 基本思想是利用射线法，计算射线与多边形各边的交点，如果是偶数，则点在多边形外，否则
 * 在多边形内。还会考虑一些特殊情况，如点在多边形顶点上，点在多边形边上等特殊情况。
 * @param $point array 指定点坐标 $point = ['lng'=>121.427417,'lat'=>31.20357];
 * @param $pts array 多边形坐标,顺时针方向 $pts = [['lng'=>121.23036,'lat'=>31.218609],['lng'=>121.233666,'lat'=>31.210579],['lng'=>121.247177,'lat'=>31.206749],['lng'=>121.276353,'lat'=>31.190811],['lng'=>121.267442,'lat'=>31.237383]];
 * @return bool
 */
function is_point_in_polygon($point, $pts) {
    $N = count($pts);
    $boundOrVertex = true; //如果点位于多边形的顶点或边上，也算做点在多边形内，直接返回true
    $intersectCount = 0;//cross points count of x
    $precision = 2e-10; //浮点类型计算时候与0比较时候的容差
    $p1 = 0;//neighbour bound vertices
    $p2 = 0;
    $p = $point; //测试点

    $p1 = $pts[0];//left vertex
    for ($i = 1; $i <= $N; ++$i) {//check all rays
        // dump($p1);
        if ($p['lng'] == $p1['lng'] && $p['lat'] == $p1['lat']) {
            return $boundOrVertex;//p is an vertex
        }

        $p2 = $pts[$i % $N];//right vertex
        if ($p['lat'] < min($p1['lat'], $p2['lat']) || $p['lat'] > max($p1['lat'], $p2['lat'])) {//ray is outside of our interests
            $p1 = $p2;
            continue;//next ray left point
        }

        if ($p['lat'] > min($p1['lat'], $p2['lat']) && $p['lat'] < max($p1['lat'], $p2['lat'])) {//ray is crossing over by the algorithm (common part of)
            if($p['lng'] <= max($p1['lng'], $p2['lng'])){//x is before of ray
                if ($p1['lat'] == $p2['lat'] && $p['lng'] >= min($p1['lng'], $p2['lng'])) {//overlies on a horizontal ray
                    return $boundOrVertex;
                }

                if ($p1['lng'] == $p2['lng']) {//ray is vertical
                    if ($p1['lng'] == $p['lng']) {//overlies on a vertical ray
                        return $boundOrVertex;
                    } else {//before ray
                        ++$intersectCount;
                    }
                } else {//cross point on the left side
                    $xinters = ($p['lat'] - $p1['lat']) * ($p2['lng'] - $p1['lng']) / ($p2['lat'] - $p1['lat']) + $p1['lng'];//cross point of lng
                    if (abs($p['lng'] - $xinters) < $precision) {//overlies on a ray
                        return $boundOrVertex;
                    }

                    if ($p['lng'] < $xinters) {//before ray
                        ++$intersectCount;
                    }
                }
            }
        } else {//special case when ray is crossing through the vertex
            if ($p['lat'] == $p2['lat'] && $p['lng'] <= $p2['lng']) {//p crossing over p2
                $p3 = $pts[($i+1) % $N]; //next vertex
                if ($p['lat'] >= min($p1['lat'], $p3['lat']) && $p['lat'] <= max($p1['lat'], $p3['lat'])) { //p.lat lies between p1.lat & p3.lat
                    ++$intersectCount;
                } else {
                    $intersectCount += 2;
                }
            }
        }
        $p1 = $p2;//next ray left point
    }

    if ($intersectCount % 2 == 0) {//偶数在多边形外
        return false;
    } else { //奇数在多边形内
        return true;
    }
}

/**
 * 格式化区域坐标为is_point_in_polygon函数的参数$pts
 *
 * @param string $area 为逗号分隔的坐标组，119.91524,31.640289,119.907946,31.640289,119.907156,31.644931
 * @return array
 */
function area2points($area = '') {
    $ret = [];
    $arr = explode(',', $area);
    $i   = 0;
    foreach ($arr as $k => $v) {
        if ($k % 2 == 0) {
            $ret[$i]['lng'] = $v;
        } else {
            $ret[$i]['lat'] = $v;
            $i++;
        }
    }
    return $ret;
}
